Electrostatic clamps or chucks (ESCs) are often utilized in the semiconductor industry for clamping workpieces or substrates during plasma-based or vacuum-based semiconductor processes such as ion implantation, etching, chemical vapor deposition (CVD), etc. Clamping capabilities of the ESCs, as well as workpiece temperature control, have proven to be quite valuable in processing semiconductor substrates or wafers, such as silicon wafers. A typical ESC, for example, comprises a dielectric layer positioned over a conductive electrode, wherein the semiconductor wafer is placed on a surface of the ESC (e.g., the wafer is placed on a surface of the dielectric layer). During semiconductor processing (e.g., ion implantation), a clamping voltage is typically applied between the wafer and the electrode, wherein the wafer is clamped against the chuck surface by electrostatic forces.
Some conventional ESCs further utilize backside gas cooling in order to cool the workpiece during processing. In such instances, a cooling gas is statically presented within a gap between the workpiece and one or more recessed surfaces of the ESC, wherein the pressure of the gas is generally proportional to the heat transfer coefficient thereof within the gap. Thus, in order to attain a higher cooling rate, a higher static backside cooling gas pressure is typically needed in order to provide the desired thermal performance. Thus, in order to maintain proper clamping of the workpiece, forces associated with the higher backside gas pressure should be properly offset with a larger clamping force or voltage applied to the ESC. In cases of high power ion implantations (e.g., 2.5 kW), the gas pressure is substantially high in order to attain proper cooling, wherein the clamping force should be appropriately increased in an attempt to compensate for the substantially high gas pressure. Further, in the case of a scanned workpiece, such as seen in some ion implantation systems, large G-forces can be present during workpiece oscillation, wherein even higher clamping forces are necessitated in order to maintain sufficient contact between the workpiece and the ESC. However, increasing the clamping force on the entire workpiece can have deleterious effects, such as increased particulate contamination, since the increased clamping pressure can cause frictional forces between the ESC and the workpiece across the surface of the workpiece, thus leading to greater chances of particulate contamination across the areas of the workpiece in which devices are formed.
Therefore, a need exists in the art for a clamp operable to constrain the workpiece, while mitigating particulate contamination, and also while providing desired temperature uniformities and clamping pressure for efficiently processing the workpiece.